Illumination optical system and projector using the same

ABSTRACT

The present invention provides a technique for readily changing the design of a projector. A projector comprises: an illumination optical system; a light modulation device; a projection optical system; and a base frame for mounting a plurality of optical components disposed on a light path from the optical illumination system to the projection optical system. The illumination optical system  300  comprises: a light source  20;  a lens array  320;  and a superimposing lens system  370.  The base frame includes a positioning section for positioning the superimposing lens system  370.  The superimposing lens system  370  includes at least two lenses  371  and  372.  The first lens  371  is provided at a position nearest to the light source and mainly determines an F-number of the illumination optical system. The second lens  372  is provided at a position furthest from the light source and mainly determines a magnification of the illumination optical system.

TECHNICAL FIELD

[0001] The present invention relates to an illumination optical systemand a projector using the same.

BACKGROUND ART

[0002]FIG. 11 is a schematic explanatory view showing a conventionalprojector. This projector comprises an illumination optical system 520,a color light separation optical system 530, a relay optical system 540,three liquid crystal panels 550R, 550G and 550B, a cross dichroic prism560, and a projection optical system 570.

[0003] The illumination optical system 520 comprises a light source unit510, a first and a second lens array 521 and 522, a polarizationconversion element 523, and a superimposing lens 524. The first lensarray 521 includes a plurality of small lenses for dividing light fromthe light source 510 into a plurality of light bundles. The second lensarray 522 and the superimposing lens 524 form images of each small lensin the first lens array on the liquid crystal panels. Also, thesuperimposing lens 524 superimposes the light bundles on the liquidcrystal panels 550R, 550G and 550B. It should be noted that thepolarization direction of the light emitted from the illuminationoptical system 520 is aligned into one type of direction by thepolarization conversion element 523.

[0004] Light W emitted from the illumination optical system 520 isseparated into the three color lights of red (R), green (G), and blue(B) at the color light separation optical system 530. Each color lightR, G and B enters each of the three liquid crystal panels 550R, 550G,550B through collimating lenses 534, 535, 536 respectively. The bluelight B passes through the relay optical system 540 to enter the liquidcrystal panel 550B. The liquid crystal panels 550R, 550G and 550Bmodulate the color lights R, G and B respectively according to givenimage information. The modulated color lights are combined by the crossdichroic prism 560, and the combined light is projected onto a screen bythe projection optical system 570.

[0005] The projector comprises a base frame (not illustrated) on whichthe above optical components are mounted. Each optical component ispositioned by means of positioning section such as a concave portion anda convex portion provided in the base frame.

[0006] By the way, the optical system and base frame are changeddepending on the projector model. For example, the projection opticalsystem and liquid crystal panels are changed depending on the model. Theillumination optical system is also changed depending on those changes.Further, the base frame is changed depending on changes to the opticalsystems in the projector. Namely, a dedicated base frame isconventionally prepared for each model having a different opticalsystem. Because of this, there was the conventional problem that designchanges for projectors required time and labor. This problem is notlimited to projectors, but is common to other systems having anillumination optical system.

DISCLOSURE OF THE INVENTION

[0007] The object of the present invention is thus to solve thedrawbacks of the prior art discussed above and to provide a techniquefor readily changing the design of apparatuses such as a projectorhaving an illumination optical system.

[0008] At least part of the above and the other related objects isattained by a first apparatus of the present invention, which is anillumination optical system for illuminating a predeterminedillumination area. The illumination optical system includes: a lightsource; a lens array including a plurality of small lenses for dividinglight emitted from the light source into a plurality of light bundles; asuperimposing lens system for superimposing the plurality of lightbundles on the predetermined illumination area; and a base frame formounting a plurality of optical components disposed at least on a lightpath from the lens array to the superimposing lens system, the baseframe including a positioning section for positioning at least thesuperimposing lens system. The superimposing lens system includes atleast two lenses including a first lens and a second lens. The firstlens is provided at a position nearest to the light source and mainlydetermines an F-number of the illumination optical system, and thesecond lens is provided at a position furthest from the light source andmainly determines a magnification of the illumination optical system.

[0009] In this illumination optical system, by changing the lensesconstituting the superimposing lens system, the F-number andmagnification of the illumination optical system can be changed withoutchanging the disposition of the superimposing lens system. Thus, it ispossible to use a common base frame with different models, the result ofwhich is that the design of the illumination optical system can bereadily changed. Also, in an apparatus such as a projector includingthis illumination optical system, the design of the apparatus can bereadily changed according to the model.

[0010] In the above apparatus, it is preferable that the superimposinglens system consists of the two lenses. In this case, the constructionof a superimposing lens system is simple, so the design of thesuperimposing lens system can be readily changed. It should be notedthat the superimposing lens system can be constructed by assemblingthree or more lenses.

[0011] In the above apparatus, a mirror for bending a travel directionof light may be disposed between the two lenses. In this case, anapparatus such as a projector including this illumination optical systemcan be constructed in a compact manner.

[0012] In the above apparatus, each lens constituting the superimposinglens system may be attached to the base frame using an elastic member.Alternatively, at least one of the plurality of lenses constituting thesuperimposing lens system may be attached to the base frame using anelastic member. In this case, it is easy to attach and remove thelenses.

[0013] In the above apparatus, at least one of the plurality of lensesconstituting the superimposing lens system may be attached to the baseframe through a holding frame for holding the lens. In this case, it iseasy to attach the lenses to the base frame.

[0014] In the above apparatus, it is preferable that a first guidingportion and a second guiding portion for guiding the holding frame tothe base frame are provided in the holding frame and the base framerespectively; a predetermined gap is formed between the two guidingportions; and a position for a direction orthogonal to an optical axisof the holding frame is adjusted within the predetermined gap, and aposition for a direction of the optical axis of the holding frame isdetermined by the positioning section. In this case, the position of thedirection orthogonal to the optical axis of the lenses constituting thesuperimposing lens can be adjusted, so when a predetermined illuminationarea and a lighting area of the illumination optical system aremisaligned vertically or horizontally, the lighting area of theillumination optical system can be aligned with the available displayarea of the liquid crystal panel.

[0015] In the above apparatus, it is preferable that the at least onelens attached to the base frame through the holding frame includes thesecond lens. The second lens positioned at the furthest position fromthe light source has the function to ultimately determine the formationposition of the lighting area of the illumination optical system. It isthus possible to align the lighting area of the illumination opticalsystem to a predetermined illumination area relatively easily.

[0016] In the above apparatus, a polarization conversion element foraligning a polarization direction of light emitted from the illuminationoptical system may be provided between the lens array and thesuperimposing lens system. In this case, the polarization direction ofthe light emitted from the illumination optical system can be aligned.When a projector includes this illumination optical system, it ispossible to use light effectively.

[0017] The present invention is also directed to a second apparatus,which is a projector that includes: an illumination optical system; alight modulation device for modulating light given from the illuminationoptical system according to image information; a projection opticalsystem for projecting the modulated light; and a base frame for mountinga plurality of optical components disposed on a light path from theoptical illumination system to the projection optical system. Theillumination optical system comprises: a light source; a lens arrayincluding a plurality of small lenses for dividing light emitted fromthe light source into a plurality of light bundles; and a superimposinglens system for superimposing the plurality of light bundles on thelight modulation device. The base frame includes a positioning sectionfor positioning at least the superimposing lens system. Thesuperimposing lens system includes at least two lenses including a firstlens and a second lens. The first lens is provided at a position nearestto the light source and mainly determines an F-number of theillumination optical system, and the second lens is provided at aposition furthest from the light source and mainly determines amagnification of the illumination optical system.

[0018] This projector includes an illumination optical system which isthe first apparatus of the present invention. The design of theprojector can thus be readily changed according to the model. It shouldbe noted that the light modulation device may be a liquid crystal panel.

[0019] The present invention is also directed to a third apparatus,which is an illumination optical system for illuminating a predeterminedillumination area. The illumination optical system includes: a lightsource; a lens array including a plurality of small lenses for dividinglight emitted from the light source into a plurality of light bundles;and a superimposing lens system for superimposing the plurality of lightbundles on the predetermined illumination area. The superimposing lenssystem includes a plurality of lenses, the plurality of lenses beingdisposed so as to be replaceable with lenses having different focallengths.

[0020] In this illumination optical system, as with the first apparatusof the present invention, the lenses constituting the superimposing lenssystem are disposed so as to be replaceable, so the design of theillumination optical system can be readily changed according to themodel. Also, if an apparatus such as a projector includes theillumination optical system, the design of the apparatus can be readilychanged according to the model.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is an explanatory view showing a projector (projectiondisplay apparatus) to which the present invention has been applied;

[0022]FIG. 2 is an explanatory view showing an illumination opticalsystem 300 indicated in FIG. 1 magnified;

[0023] FIGS. 3(A) and 3(B) are explanatory views showing the outside ofa first lens array 320;

[0024]FIG. 4 is a perspective view showing the outside of a firstpartial polarization conversion element array 361;

[0025]FIG. 5 is an explanatory view showing a part of the first partialpolarization conversion element array 361 shown in FIG. 4 magnified.;

[0026]FIG. 6 is a front view showing a shading plate 350;

[0027]FIG. 7 is an explanatory view showing a model of the function of asuperimposing lens system 370;

[0028]FIG. 8 is an explanatory view showing the condition when thesuperimposing lens system 370 is mounted on a base frame;

[0029]FIG. 9 is an explanatory view showing a superimposing lens system370A in the second embodiment;

[0030]FIG. 10 is an explanatory view showing the condition when a secondlens 372 is mounted on a base frame using a holding frame; and

[0031]FIG. 11 is a schematic explanatory view showing the conventionalprojector.

BEST MODES OF CARRYING OUT THE INVENTION

[0032] A. First Embodiment:

[0033] A-1. Entire Construction of Projector:

[0034] One mode of carrying out the present invention is discussed belowas a preferred embodiment. FIG. 1 is an explanatory view showing aprojector (projection display apparatus) to which the present inventionhas been applied. The projector comprises an illumination optical system300, a color light separation optical system 380, a relay optical system390, three liquid crystal panels 410R, 410G and 410B, a cross dichroicprism 420, and a projection optical system 40.

[0035]FIG. 2 is an explanatory view showing the illumination opticalsystem 300 shown in FIG. 1 magnified. The illumination optical system300 comprises a light source unit 20, a first and a second lens array320 and 340, a shading plate 350, a polarization conversion elementarray 360, and a superimposing lens system 370.

[0036] The light source unit 20 includes a light source lamp 210 and aconcave mirror 212. Light emitted radially (radial light) from the lightsource lamp 210 is reflected by the concave mirror 212. The reflectedlight is emitted towards the first lens array 320 as substantiallyparallel light bundle. A halogen lamp, metal halide lamp or highpressure mercury lamp may be used as the light source lamp 210. Aparabolic mirror may be used as the concave mirror 212.

[0037] The first lens array 320 has the function of dividing thesubstantially parallel light bundle emitted from the light source unit20 into a plurality of partial light bundles. FIGS. 3(A) and 3(B) areexplanatory views showing the outside of the first lens array 320. FIG.3(A) is a front view, and FIG. 3(B) is a side view. The first lens array320 has a plurality of rectangle small lenses 321 disposed in a matrixof 2×N columns (here, N=4) in the vertical direction and M rows (here,M=10) in the horizontal direction. The external shape of each small lens321 seen from the light traveling direction is substantially similar tothe external shape of the liquid crystal panel 410R, 410G, 410B as anillumination area (illuminated area). For example, when the aspect ratio(the ratio of the horizontal and vertical dimensions) of the availabledisplay area (image formation area) in the liquid crystal panel is 4:3,the aspect ratio of each small lens 321 is set to 4:3 as well.

[0038] Along with the superimposing lens system 370, the second lensarray 340 (FIG. 2) has the function of forming images from each smalllens in the first lens array on the liquid crystal panels. The secondlens array 340 is substantially same with the first lens array 320, andhas the same number of small lenses 341 as the number of small lensesconstituting the first lens array 320. The first and second lens arrays320 and 340 are referred to as integrator lenses.

[0039] The polarization conversion element array 360 (FIG. 2) includestwo partial polarization conversion element arrays 361 and 362. The twopartial polarization conversion element arrays (hereinafter, referred tosimply as “partial element arrays”) are disposed so as to be mutuallyopposing about the optical axis. It should be noted that the followingdescription is given focusing on the first partial element array 361,but the second partial element array 362 is similar.

[0040]FIG. 4 is a perspective view showing the outside of the firstpartial polarization conversion element array 361. The first partialelement array 361 includes a polarization beam splitter array 363, and aλ/2 retardation plate 364 (λ is the wavelength of the light) selectivelydisposed on the light exiting face of the polarization beam splitterarray 363. The polarization beam splitter array 363 is formed by joininga plurality of columnar transmissive members 365 with a parallelogramcross-section placed. A polarization splitting film 366 and a reflectingfilm 367 are formed alternately at the boundary face of eachtransmissive member 365. The λ/2 retardation plates 364 are selectivelyattached to areas corresponding to the polarization splitting films 366.

[0041] The partial element array 361 has the function of convertingnon-polarized incident light into one type of linearly polarized light(s-polarized light or p-polarized light) and then emitting the linearlypolarized light. FIG. 5 is an explanatory view showing a part of thefirst partial polarization conversion element array 361 shown in FIG. 4magnified. Non-polarized light (the light having random polarizationdirections) including s-polarization component and p-polarizationcomponent enters the light incident surface of the partial element array361. The non-polarized light is separated into s-polarized light andp-polarized light by the polarization splitting film 366. Thes-polarized light is reflected by the polarization splitting film 366,reflected again by the reflecting film 367, and then emitted. Thep-polarized light, on the other hand, passes through the polarizationsplitting film 366, is converted to s-polarized light by the λ/2retardation plate 364, and then emitted. Thus, only s-polarized light isemitted from the partial element array 361. To emit only p-polarizedlight from the partial element array 361, λ/2 retardation plates 364 maybe selectively disposed in areas corresponding to the reflecting films367. Also, a λ/4 retardation plate may be used in place of the λ/2retardation plate 364 to align the direction of polarization. Also,appropriate retardation plates may be provided at the exiting face forthe p-polarized light and the exiting face for the s-polarized face toalign the direction of polarization.

[0042] As shown in FIG. 4, a block including one set of adjacentpolarization splitting film 366 and reflecting film 367 as well as oneλ/2 retardation plate 364 may be considered one polarization conversionelement 368. The first partial polarization conversion element array 361is constructed by disposing a plurality of these polarization conversionelements 368 orthogonal to the light traveling direction.

[0043] The shading plate 350 (FIG. 2) has the function of allowing lightto enter only areas in the incident surface of the polarizationconversion element array 360 that correspond to the polarizationsplitting films 366. FIG. 6 is a front view showing the shading plate350. The shading plate 350 is constructed by providing a plurality ofopenings 351 in the substantially rectangle shaped plate.

[0044] The superimposing lens system 370 (FIG. 2) includes two lenses371 and 372 disposed at a predetermined distance, and has the functionof causing a plurality of partial light bundles emitted from thepolarization conversion element array 360 to be superimposed on theliquid crystal panels 410R, 410G and 410B. As shown in FIG. 1, in theillumination optical system 300 of this embodiment, a mirror 379 isdisposed between the first lens 371 and the second lens 372. The mirror379 causes light emitted from the first lens 371 to bend atsubstantially a right angle, and leads it toward the color lightseparation optical system 380. In this manner, the mirror 379 is used toconstruct a projector in a compact manner. If bending the lighttraveling direction is not necessary, the mirror 379 will be omitted.

[0045] As described above, substantially parallel light bundle emittedfrom the light source 20 are divided into a plurality of partial lightbundles 202 by the first lens array 320. Then, each of the partial lightbundles 202 passes through the second lens array 340, and is focused inthe vicinity of the polarization splitting film 366 of the polarizationconversion element array 360. The plurality of partial light bundlesentering the polarization conversion element array 360 are converted toone type of linearly polarized light and then emitted. The plurality ofpartial light bundles emitted from the polarization conversion elementarray 360 are superimposed on the liquid crystal panels 410R, 410G and410B by the superimposing lens system 370. In this embodiment, lightemitted from the illumination optical system is aligned in one type ofpolarization direction, so it is possible to use the light effectivelyin the liquid crystal panels.

[0046] The color light separation optical system 380 (FIG. 1) includestwo dichroic mirrors 382, 386 and a reflecting mirror 384, and has thefunction of separating light emitted from the illumination opticalsystem 300 into the three color lights of red, green and blue. The firstdichroic mirror 382 allows the red component from the light emitted fromthe illumination optical system 300 to pass through, while reflectingthe blue component and the green component. The red light passingthrough the first dichroic mirror 382 is reflected by the reflectingmirror 384, and passes through a collimating lens 400 to reach theliquid crystal panel 410R for red light. The collimating lens 400 hasthe function of converting each partial light bundle emitted from theillumination optical system 300 into a partial light bundle parallel tothe principal ray (center ray). Collimating lenses 402 and 404 providedat the light incident surface of the other liquid crystal panels 410Gand 410B are similar.

[0047] Of the light which includes the blue component and the greencomponent reflected by the first dichroic mirror 382, the green lightreflected by the second dichroic mirror 386 passes through thecollimating lens 402 to reach the liquid crystal panel 410G for greenlight. The blue light, on the other hand, which passes through thesecond dichroic mirror 386, passes through the relay optical system 390,or more specifically, the incident side lens 392, the first reflectingmirror 394, the relay lens 396 and the second reflecting mirror 398,then further passes through the collimating lens 404 to reach the liquidcrystal panel 410B for blue light. The relay optical system is providedto prevent the optical efficiency of the blue light from decreasing dueto light diverging.

[0048] The three liquid crystal panels 410R, 410G, 410B are lightmodulation devices (light modulation elements) having the function ofmodulating light according to given image information (image signals).Each color light entering each of the three liquid crystal panels ismodulated according to the given image information, and an image isformed in each color. It should be noted that polarizing plates notillustrated are provided at the light incident side and the lightexiting side of each liquid crystal panel. A set of a liquid crystalpanel and two polarizing plates is referred to as a liquid crystal lightvalve.

[0049] The three modulated color lights emitted from the three liquidcrystal panels 410R, 410G, 410B enter the cross dichroic prism 420. Thecross dichroic prism 420 combines the three modulated color lights andgenerates a combined light showing a color image. In other words, thecross dichroic prism 420 functions as a color light combining prism. Thecombined light is emitted in the direction of an entrance pupil of theprojection optical system 40.

[0050] The projection optical system 40 is an assembly having aplurality of lenses. The projection optical system 40 projects thecombined light obtained by the cross dichroic prism 420 onto a screen. Acolor image is thereby displayed on the screen.

[0051] As mentioned above, the projector comprises a plurality ofoptical components (optical elements). The projector also comprises abase frame (referred to also as a “light guide”) for mounting theplurality of optical components. The positioning of each of theplurality of optical components is determined by a convex portion or aconcave portion provided in the base frame. The base frame will bedescribed later.

[0052] A-2. Design of Illumination Optical System:

[0053] As described above, the optical system of a projector is changeddepending on the projector model. For example, the projection opticalsystem and the liquid crystal panels are changed depending on the model.And with that change, the F-number and magnification of the illuminationoptical system change. Conventionally, the base frame is also changedwhen there is a change in the optical system of the projector. Morespecifically, conventionally, a dedicated base frame is prepared foreach model having a different optical system. In this manner, adedicated base frame is needed in a conventional projector, because thesuperimposing lens system comprises only one superimposing lens 524 asshown in FIG. 11. In other words, when the F-number and magnification ofthe illumination optical system are changed, the curvature of thesuperimposing lens 524 needs to be changed as well as its disposition.However, in a base frame where the layout of many optical components isalready decided, it is difficult to change the disposition of thesuperimposing lens 524 without interfering with the other opticalcomponents. In this manner, there is an extremely low degree of freedomto change the design of a conventional projector.

[0054] In the projector of this embodiment, the superimposing lenssystem comprises two lenses 371 and 372, thereby improving the degree offreedom to change the design. Concretely, it is possible to change theF-number or magnification of the illumination optical system withoutchanging the position of the lenses constituting the superimposing lenssystem. It is thus possible to use a common base frame for differentmodels, and as a result, the design of the projector can be readilychanged.

[0055]FIG. 7 is an explanatory view showing a model of the function ofthe superimposing lens system 370. As illustrated, the two lensesconstituting the superimposing lens system 370 are provided separated bya predetermined distance D.

[0056] The F-number of the illumination optical system 300 isrepresented by about f0/(2×d). Here, “f0” is the distance from theprincipal point (second principal point) H of the superimposing lenssystem 370 to the focal point in image space(liquid crystal panels 410R,410G, 410B). “2×d” is the dimension (width) of the light bundle and isdetermined by the light source unit 20. More specifically, thesuperimposing lens system 370 constituted of the two lenses 371 and 372is equivalent to a hypothetical lens (condenser lens) having one focallength f0, provided between the two lenses.

[0057] For example, if the surface of the second lens 372 is assumed tobe flat having a curvature of zero, the position of the hypotheticallens will be that of the first lens 371. In this case, the F-number ofthe illumination optical system will be represented by about f1/(2×d).It should be noted that “f1” is the distance from the first lens 371 tothe liquid crystal panels 410R, 410G and 410B, and is the focal lengthof the first lens 371 in this hypothetical example. On the other hand,if the surface of the first lens 371 is assumed to be flat having acurvature of zero, the position of the hypothetical lens will be that ofthe second lens 372. In this case, the F-number of the illuminationoptical system will be represented by about f2/(2×d). It should be notedthat “f2” is the distance from the second lens 372 to the liquid crystalpanels 410R, 410G and 410B, and is the focal length of the second lens372 in this hypothetical example.

[0058] As will be appreciated from the above description, the positionof the hypothetical lens can be set to a desired position between thetwo lenses 371 and 372 by changing the curvature of the surface of thetwo lenses 371 and 372. In other words, by changing the focal lengths ofthe two lenses 371 and 372, it is possible to set the F-number of theillumination optical system to a desired value without changing thedisposition of the two lenses. When employing a negative lens, theposition of the hypothetical lens may be set to a position external tothe two lenses.

[0059] Below, cases are described where the projection optical systemand the liquid crystal panels are changed according to the model.

[0060] (a) When changing the F-number of the projection optical system40 according to the model, the F-number of the illumination opticalsystem 300 also needs to be changed. Namely, the F-number of theprojection optical system 40 is set nearly the same as the F-number ofthe illumination optical system 300 or therebelow. In this case, theprojection optical system has an aperture nearly equivalent to or higherthan the illumination optical system 300.

[0061] When the F-number of the projection optical system 40 isdecreased, the F-number of the illumination optical system 300 is alsodecreased. Specifically, the focal length of the first lens 371constituting the superimposing lens system 370 is set to a relativelylarge value. The focal length of the second lens 372 is preferably setto a relatively small value. In this case, the position of thehypothetical lens will be set relatively near the liquid crystal panels,and the F-number of the illumination optical system will be set small.

[0062] It should be noted that the focal length of a lens can beadjusted by changing the refractive index or the curvature of the lens.For example, when setting the focal length of a lens relatively short,the refractive index of the lens will be made large or the curvature(=1/radius) of the lens will be made large.

[0063] (b) When the structure of the liquid crystal panels 410R, 410Gand 410B is changed according to the model, it is necessary to changethe F-number of the illumination optical system 300. The liquid crystalpanels may be internally equipped with micro-lenses to increase theamount of light passing through.

[0064] When the liquid crystal panels include micro-lenses, the F-numberof the illumination optical system 300 is set relatively large.Specifically, the focal length of the first lens 371 is set to arelatively small value. The focal length of the second lens 372 ispreferably set to a value larger than the focal length of the first lens371. In this case, the position of the hypothetical lens will be setrelatively far from the liquid crystal panels, and the F-number of theillumination optical system will be set large. As a result, the apertureof the illumination optical system can be constrained while diffusion oflight is prevented from occurring in the micro-lenses.

[0065] When the liquid crystal panels do not include micro-lenses, onthe other hand, the F-number of the illumination optical system 300 isset relatively small. Specifically, the focal length of the first lens371 is set to a relatively large value. The focal length of the secondlens 372 is preferably set to a value smaller than the focal length ofthe first lens 371. In this case, the position of the hypothetical lenswill be set relatively near the liquid crystal panels, and the F-numberof the illumination optical system will be set small. As a result, theliquid crystal panels can use illumination light effectively.

[0066] (c) When the size of the liquid crystal panels is changedaccording to the model, it is necessary to change the magnification ofthe illumination optical system 300. Here, the magnification of theillumination optical system 300 means the ratio of the size of theliquid crystal panel 410R, 410G, 410B to the small lens 321 of the firstlens array 320. When the focal length of the small lens 321 of the firstlens array is fa, the magnification is represented by about f0/fa.

[0067] When the size of the liquid crystal panels is increased, themagnification of the illumination optical system 300 also needs to beincreased. Specifically, the focal length of the second lens 372 is setto a relatively large value. The focal length of the first lens 371 ispreferably set to a relatively small value. On the other hand, when thesize of the liquid crystal panels is decreased, the magnification of theillumination optical system 300 also needs to be decreased.Specifically, the focal length of the second lens 372 is set to arelatively small value. The focal length of the first lens 371 ispreferably set to a relatively large value.

[0068] It should be noted that when the size of the liquid crystalpanels is changed according to the model, the focal length of each lensconstituting the superimposing lens system 370 may be changed, and themagnification of the illumination optical system may also be changed bychanging the size and the focal length of the small lenses 321 in thefirst lens array 320.

[0069] In this manner, when the F-number of the illumination opticalsystem 300 is changed, the focal length of the first lens 371 providedat a position relatively near the light source unit 20 is mainlychanged. Also, when the magnification of the illumination optical system300 is changed, the focal length of the second lens 372 provided at aposition relatively far from the light source unit 20 is mainly changed.This is because the first lens 371 has a higher ability than the secondlens 372 to change the F-number of the illumination optical system 300,and the second lens 372 has a higher ability than the first lens 371 tochange the magnification of the illumination optical system 300. Inother words, the first lens 371 provided at a position relatively nearthe light source 20 has the function to mainly determine the F-number ofthe illumination optical system, and the second lens 372 provided at arelatively far position has the function to mainly determine themagnification of the illumination optical system.

[0070]FIG. 8 is an explanatory view showing the condition when thesuperimposing lens system 370 is mounted on the base frame. Asillustrated, in this embodiment, the two lenses 371 and 372 constitutingthe superimposing lens system 370 are fixed inside the cabinet of theprojector to the base frame 100 so as to be attachable and detachable.Concretely, the base frame 100 is provided with two grooves 110, 130 andtwo erect walls 120, 140 as positioning sections to position the twolenses 371, 372. The distance between the two grooves 110, 130 and thedistance between the two erect walls 120, 140 are set to a predetermineddistance D (FIG. 7). The first lens 371 is fixed by an elastic clip 160holding the erect wall 120 and the first lens 371. Similarly, the secondlens 372 is fixed by an elastic clip 170 holding the erect wall 140 andthe second lens 372. The erect walls 120, 140 have openings 121, 141 toallow light to pass through.

[0071] In this manner, the elastic force of elastic member is used tomount the lenses 371, 372 constituting the superimposing lens system 370to the base frame 100 so as to be attachable and detachable, therebyallowing the lenses 371, 372 to be replaced by lenses having a differentfocal length (having a different curvature).

[0072] As described above, a projector of this embodiment comprises anillumination optical system 300, liquid crystal panels 410R, 410G, 410Bfor modulating light provided by the illumination optical systemaccording to image information, a projection optical system 40 forprojecting the modulated light, and a base frame 100 on which theplurality of optical components on the light path from the illuminationoptical system to the projection optical system are disposed. Theillumination optical system 300 comprises a light source unit 20, afirst lens array 320 including a plurality of small lenses 321 fordividing light emitted from the light source unit into a plurality oflight bundles; and a superimposing lens system 370 for superimposing theplurality of light bundles on the liquid crystal panels. The base frame100 includes positioning sections such as grooves 110, 130 and erectwalls 120, 140 for positioning the superimposing lens system. Thesuperimposing lens system 370 consists of two lenses 371 and 372, andthe first lens 371 is provided at a position relatively near the lightsource unit 20 mainly to determine the F-number of the illuminationoptical system, and the second lens 372 is provided at a positionrelatively far from the light source unit 20 mainly to determine themagnification of the illumination optical system.

[0073] In this embodiment, the plurality of optical components disposedon the light path from the illumination optical system to the projectionoptical system are mounted on the base frame 100, but instead, a partialbase frame may be used for mounting only the illumination opticalsystem. In this case, the plurality of optical components disposed atleast on the light path from the first lens array to the superimposinglens system are mounted on the partial base frame. The partial baseframe is then mounted on the overall base frame.

[0074] In a projector such as mentioned above, the focal length of thelenses constituting the superimposing lens system may be changedaccording to changes in the projection optical system and liquid crystalpanels, so that the F-number and the magnification of the illuminationoptical system 300 can be changed without changing the disposition ofthe superimposing lens system 370. Accordingly, it is possible to use acommon base frame for different models, and as a result, the design ofthe projector can be readily changed. There is also the advantage thatthe size of the optical system of the projector overall need not bechanged for changes in the illumination optical system.

[0075] In a conventional projector, the superimposing lens systemconsists of only one lens. In this case, the lens tends to be thicker.When the lens is thicker, a misalignment of the displayed imagesometimes occurs due to an aberration. However, in this embodiment, thesuperimposing lens system consists of two relatively thin lenses, so theaberration is small, and misalignment of the displayed image can bedecreased.

[0076] Also, regardless of the fact that the magnification of theillumination optical system is determined such that the entire availabledisplay area of the liquid crystal panel is lighted, in actuality, aso-called display shadow occurs without the entire available displayarea being lighted. In such cases, the magnification of the illuminationoptical system can be changed by changing the F-number of theillumination optical system to adjust the light so as to enter theentire available display area of the liquid crystal panels. Namely, itis possible to substantially change the magnification of theillumination optical system by changing the F-number of the illuminationoptical system.

[0077] B. Second Embodiment:

[0078]FIG. 9 is an explanatory view showing a superimposing lens system370A in the second embodiment. This superimposing lens system 370Aconsists of three lenses. Specifically, a third lens (concave lens) 373is added between the two lenses 371, 372 of the first embodiment. Inthis manner, it is possible to construct the superimposing lens system370A with three or more lenses. In general, at least two lenses shouldbe included in the superimposing lens system. Constructing thesuperimposing lens system with two lenses as in the first embodiment hasthe advantage that because the construction is simple, the design of thesuperimposing lens system can be easily changed.

[0079] When the superimposing lens system comprises three or morelenses, it is preferable to provide the first lens mainly fordetermining the F-number of the illumination optical system at theposition nearest the light source unit and to provide the second lensmainly for determining the magnification of the illumination opticalsystem at the position furthest from the light source unit.

[0080] Also, it is preferable if each lens constituting thesuperimposing lens system is provided so as to be attachable to anddetachable from the base frame so they can be readily replaced.

[0081] C. Third Embodiment:

[0082] In the first embodiment, the lenses 371 and 372 constituting thesuperimposing lens system 370 are directly mounted on the base frame100, but instead, they may be mounted using a holding frame.

[0083]FIG. 10 is an explanatory view showing the condition of the secondlens 372 mounted on the base frame using a holding frame. Asillustrated, the second lens 372 is held by a holding frame 70.Concretely, the circumferential edge of the second lens 372 is fittedinto the holding frame 70, and the bottom is held by a clip 79.

[0084] Engaging portions (first guiding portions) 71 are provided onboth side faces of the holding frame 70 to guide the holding frame 70 inthe base frame 100A. Corresponding thereto, two catching portions(second guiding portions) 101 for engaging with the two engagingportions 71 on the holding frame 70 are formed on the base frame 100A.The catching portions 101 are formed in a slit shape opening upward. Theengaging portions 71 are inserted inside the catching portions 101 fromabove, and play (a gap) is formed between the engaging portions 71 andthe catching portions 101. Specifically, play is formed in the verticaldirection and the horizontal direction (in other words, directionsorthogonal to the optical axis) between the engaging portions 71 and thecatching portions 101. No play is provided in the lateral direction (inother words, in the direction of the optical axis) between the engagingportions 71 and the catching portions 101. It is desirable to set thedimensions of play to ±1 mm through ±2 mm in the horizontal direction.

[0085] Two columnar convex portions 72 are provided on the undersideface of the holding frame 70. Corresponding thereto, two long holes 102for engaging the two convex portions 72 on the holding frame 70 areprovided on the bottom face of the base frame 100A. The short sides ofthe long hole 102 are set up in the direction of the optical axis, andthe long sides are set up in the direction orthogonal to the opticalaxis. The dimension of the short side of the long hole 102 is set nearlyequivalent to the diameter dimension of the columnar convex portions 72.

[0086] Two holes 73 making handling of the holding frame possible with ajig are provided at the top face of the holding frame 70. The tips of apair of claws 90 constituting the jig are inserted into the two holes 73respectively. The jig can grasp and release the holding frame 70 bywidening and narrowing the tips of the pair of claws 90.

[0087] When the holding frame 70 is mounted on the base frame 100A bymeans of the jig, the engaging portions 71 of the holding frame 70engage the catching portions 101 of the base frame 100A, and the convexportions 72 of the holding frame 72 engage the long holes 102 of thebase frame 100A. At this time, the holding frame 70 (the second lens372) can move by just the amount of play in the direction orthogonal tothe direction of the optical axis with respect to the base frame 100A,and movement in the direction of the optical axis is restrained. Bymoving the holding frame 70 in the direction orthogonal to the directionof the optical axis, the position of the second lens is adjusted. Thispositioning adjustment work may be carried out by, for example,operating a movement apparatus for moving the jig in three dimensions.

[0088] When the positioning adjustment of the second lens is complete,the holding frame 70 is fixed to the base frame 100A. Specifically,concave portions 75 in which adhesive material is filled are formed atthe side faces of the engaging portions 71 (the side faces adjacent tothe catching portions 101), and the engaging portions 71 and thecatching portions 101 are adhered fixedly by filling the concaveportions 75 with adhesive material.

[0089] As described above, in this embodiment, the second lens 372 isattached to the base frame though the holding frame 70. By doing this,the lenses constituting the superimposing lens system can be readilyattached to the base frame.

[0090] Also, in this embodiment, two engaging portions 71 and twocatching portions 101 for guiding the holding frame to the base frameare provided on the holding frame 70 and the base frame 100A,respectively, and a predetermined gap (play) is formed between theengaging portions 71 and the catching portions 101. The position for thedirection orthogonal to the optical axis of the holding frame 70 isadjusted within the predetermined gap, and the position for thedirection of the optical axis of the holding frame 70 is determined bythe two catching portions 101 and the two long holes 102.

[0091] By employing such a construction, the position for the directionorthogonal to the optical axis of the lens 372 constituting thesuperimposing lens system 370 can be adjusted. So when there is amisalignment between the available display area of the liquid crystalpanels and the lighting area of the illumination optical system in thevertical direction or the horizontal direction, it is possible to alignthe lighting area of the illumination optical system to the availabledisplay area of the liquid crystal panels, and as a result, the opticalefficiency is increased.

[0092] In this embodiment, the holding frame 70 is applied to the secondlens 372 constituting the superimposing lens system 370, but it may besimilarly applied to the first lens 371 as well. Alternatively, anelastic member may be used as in the first embodiment to directly mountthe first lens 371 on the base frame 100. In general, the holding frameis preferably applied to at least the second lens 372 provided at theposition furthest from the light source. This is because the second lens372 provided at the furthest position from the light source has thefunction of ultimately determining the formation position of thelighting area of the illumination optical system. By doing this, thelighting area of the illumination optical system may be alignedrelatively easily with the available display area of the liquid crystalpanels.

[0093] The present invention is not restricted to the above embodimentor its modifications, but there may be many other modifications,changes, and alterations without departing from the scope or spirit ofthe main characteristics of the present invention. Some examples ofpossible modification are given below.

[0094] (1) In the above embodiments, a dichroic prism in which two typesof color selecting faces are formed along the adhesion faces of fourrectangular prisms is used as a color light combining optical system;but instead, a combination of dichroic prisms in which one type of colorselecting face is formed, polarizing beam splitters and the like may beused. Also, a light selecting face may be provided inside asubstantially hexahedral translucent box, and a dichroic prism formed byfilling the inside of the box with a liquid.

[0095] (2) In the above embodiments, the present invention is applied toa projector using transmissive type liquid crystal panels, but thepresent invention may be applied to a projector using reflective typeliquid crystal panels as well. Also, instead of liquid crystal panels, amicromirror type light modulation device may be used. In general, alight modulation device will modulate light provided by the illuminationoptical system according to image information.

[0096] (3) In the above embodiments, the present invention is applied toa projector displaying a color image, but the present invention may beapplied to a projector displaying a monochrome image as well.

[0097] (4) For the projector, there are both a forward projectingdisplay apparatus which projects an image from the direction of theobservation and a backward projecting display apparatus which projectsan image in the reverse direction of observation; the present inventionmay be applied to either.

Industrial Applicability

[0098] The present invention may be applied to a variety of apparatusessuch as an illumination optical system and a projector using thatillumination optical system.

What is claimed is:
 1. An illumination optical system for illuminating apredetermined illumination area comprising: a light source; a lens arrayincluding a plurality of small lenses for dividing light emitted fromthe light source into a plurality of light bundles; a superimposing lenssystem for superimposing the plurality of light bundles on thepredetermined illumination area; and a base frame for mounting aplurality of optical components disposed at least on a light path fromthe lens array to the superimposing lens system, the base frameincluding a positioning section for positioning at least thesuperimposing lens system, wherein the superimposing lens systemcomprises at least two lenses including a first lens and a second lens,the first lens being provided at a position nearest to the light sourceand mainly determining an F-number of the illumination optical system,and the second lens being provided at a position furthest from the lightsource and mainly determining a magnification of the illuminationoptical system.
 2. The illumination optical system according to claim 1,wherein the superimposing lens system consists of the two lenses.
 3. Theillumination optical system according to claim 2, further comprising: amirror for bending a travel direction of light, the mirror disposedbetween the two lenses.
 4. The illumination optical system according toclaim 1, wherein each lens constituting the superimposing lens system isattached to the base frame using an elastic member.
 5. The illuminationoptical system according to claim 1, wherein at least one of theplurality of lenses constituting the superimposing lens system isattached to the base frame using an elastic member.
 6. The illuminationoptical system according to claim 1, wherein at least one of theplurality of lenses constituting the superimposing lens system isattached to the base frame through a holding frame for holding the lens.7. The illumination optical system according to claim 6, wherein a firstguiding portion and a second guiding portion for guiding the holdingframe to the base frame are provided in the holding frame and the baseframe respectively; a predetermined gap is formed between the twoguiding portions; and a position for a direction orthogonal to anoptical axis of the holding frame is adjusted within the predeterminedgap, and a position for a direction of the optical axis of the holdingframe is determined by the positioning section.
 8. The illuminationoptical system according to claim 7, wherein the at least one lensattached to the base frame through the holding frame includes the secondlens.
 9. The illumination optical system according to claim 1, furthercomprising: a polarization conversion element, provided between the lensarray and the superimposing lens system, for aligning a polarizationdirection of light emitted from the illumination optical system,.
 10. Aprojector comprising: an illumination optical system; a light modulationdevice for modulating light given from the illumination optical systemaccording to image information; a projection optical system forprojecting the modulated light; and a base frame for mounting aplurality of optical components disposed on a light path from theoptical illumination system to the projection optical system, whereinthe illumination optical system comprises: a light source; a lens arrayincluding a plurality of small lenses for dividing light emitted fromthe light source into a plurality of light bundles; and a superimposinglens system for superimposing the plurality of light bundles on thelight modulation device, wherein the base frame includes a positioningsection for positioning at least the superimposing lens system; and thesuperimposing lens system comprises at least two lenses including afirst lens and a second lens; the first lens being provided at aposition nearest to the light source and mainly determining an F-numberof the illumination optical system, and the second lens being providedat a position furthest from the light source and mainly determining amagnification of the illumination optical system.
 11. The projectoraccording to claim 10, wherein the superimposing lens system consists ofthe two lenses.
 12. The projector according to claim 11, furthercomprising: a mirror for bending a travel direction of light, the mirrordisposed between the two lenses.
 13. The projector according to claim12, wherein each lens constituting the superimposing lens system isattached to the base frame using an elastic member.
 14. The projectoraccording to claim 10, wherein at least one of the plurality of lensesconstituting the superimposing lens system is attached to the base frameusing an elastic member.
 15. The projector according to claim 10,wherein at least one of the plurality of lenses constituting thesuperimposing lens system is attached to the base frame through aholding frame for holding the lens.
 16. The projector according to claim15, wherein a first guiding portion and a second guiding portion forguiding the holding frame to the base frame are provided in the holdingframe and the base frame respectively; a predetermined gap is formedbetween the two guiding portions; and a position for a directionorthogonal to an optical axis of the holding frame is adjusted withinthe predetermined gap, and a position for a direction of the opticalaxis of the holding frame is determined by the positioning section. 17.The projector according to claim 16, wherein the at least one lensattached to the base frame through the holding frame includes the secondlens.
 18. The projector according to claim 10, further comprising: apolarization conversion element, provided between the lens array and thesuperimposing lens system, for aligning a polarization direction oflight emitted from the illumination optical system.
 19. The projectoraccording to claim 10, wherein the light modulation device is a liquidcrystal panel.
 20. An illumination optical system for illuminating apredetermined illumination area comprising: a light source; a lens arrayincluding a plurality of small lenses for dividing light emitted fromthe light source into a plurality of light bundles; and a superimposinglens system for superimposing the plurality of light bundles on thepredetermined illumination area, wherein the superimposing lens systemincludes a plurality of lenses, the plurality of lenses being disposedso as to be replaceable with lenses having different focal lengths.